The near-collapse of nuclear talks with Iran has ushered in what experts on Wednesday described as a dangerous new phase in the decade-long standoff over Tehran’s nuclear program.

A new round of sanctions is scheduled to take effect July 1, increasing the pressure on Iran’s faltering economy. At the same time, prominent Israeli and U.S. politicians are renewing calls for preparations for a military strike to halt Iran’s nuclear progress.

Iranian officials sounded fresh notes of defiance a day after talks concluded in Moscow, blaming Western countries for the lack of progress and insisting that no amount of pressure would persuade Iran to give up its right to a civilian nuclear energy program. The negotiations between Iran and the bloc of countries known as the P5-plus-1 ended late Tuesday with no agreement and no further substantive talks scheduled, other than technical consultations.

“There is not a one of us who is not aware how serious this is,” said a senior Obama administration official, reflecting on the failure to achieve any meaningful agreement with Tehran after three rounds of direct negotiations with Iranian officials since April.

While insisting that diplomatic efforts would continue, the official said the White House was “sober” in assessing the outcome of the Moscow talks, in which Iran was said to have balked at demands for freezing production of a type of enriched uranium that can be easily converted to fuel for nuclear weapons. The United States and its allies contend that Iran is using civilian facilities as a cover for developing a nuclear weapons capability, an assertion Iran denies.

The counterproposals from the Iranian side were “far from where the rest of us are,” leading to the decision to hold low-level technical consultations next month in Turkey so the sides can clarify their positions, said the official, who insisted on anonymity in describing the diplomatically sensitive negotiations.

The United States and other members of the six-nation bloc (the U.N. Security Council’s five permanent members and Germany) pushed hard in the final hours of the Moscow meeting to preserve at least an appearance of continuing negotiations, fearing that a complete failure would increase the likelihood of a military strike. But U.S. officials said they would not agree to open-ended talks that allow Iran to continue adding to its uranium stockpile. “This is not indefinite,” the administration official said.

Iran had sought relief from potentially crippling sanctions as a condition for any concessions on curbs to its nuclear program.

With diplomacy in tatters, Tehran faces the full brunt of a European Union oil embargo on July 1 and new U.S. sanctions targeting the country’s central bank.

Economists and Middle Eastern analysts say the new sanctions are likely to drain billions of dollars from the country’s economy and increase the pressure on Iran’s currency, the rial, which has lost half its value over the past year.

Worsening economic hardship could drive Iran’s leaders to adopt more aggressive and confrontational policies in the region and perhaps beyond, Iran experts warned.

“A provocative unpredictability will probably become more prominent in Iran’s foreign policy,” said Cliff Kupchan, a former State Department official and Middle East analyst for the Eurasian Group.

After months of relative quiet, he said, Tehran could revert to the aggressive behavior it displayed late last year when it threatened to shut down shipping in the Strait of Hormuz.

“The risk is that an Iranian foreign policy based on weakness and anger emerges,” he said.

Iranian officials scoffed Wednesday at the impact of new sanctions, saying they were ready to weather years of hardship if necessary.

In Washington, the faltering of diplomacy sparked renewed debate over the possibility of a military strike to halt Iran’s nuclear progress.

At a congressional hearing Wednesday, lawmakers from both parties suggested that the Pentagon should begin preparations for military action as a means of demonstrating seriousness to Iran.

Former senator Charles S. Robb (D-Va.), testifying before the House Armed Services Committee, said the preparations should include expedited deployment of new bunker-busting munitions designed to penetrate Iran’s underground nuclear bunkers.

“It is only the credible threat of force, combined with sanctions, that affords any realistic hope of an acceptable diplomatic solution,” said Robb, who co-wrote a study on Iran strategy for the Bipartisan Policy Center.

But others cautioned that a military strike would be costly and would probably only delay Iran’s pursuit of nuclear technology — not stop it.

“It is premature to conclude that a military strike is immediately required,” said the top Democrat on the committee, Rep. Adam Smith (Wash.).

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